Hurricane damage to residential and commercial buildings is a major problem, particularly in coastal regions. For example, Hurricane Andrew which hit Florida in 1992 caused tens of billions of dollars in property damage. A large amount of hurricane damage to buildings is caused by penetration of the building envelope, allowing forceful winds and weather to penetrate or enter the interior of the building. In a typical hurricane scenario, high winds initially throw debris through a building window. The wind then enters through the broken window, increasing internal air pressure within the building. The increased internal pressure places extremely high stresses on the walls and roof, typically causing the remainder of the windows to blow out and, in some cases, the roof to blow off. Hurricanes also exhibit a push-pull effect which creates an alternating pressure differential inside and outside the building.
Recognizing the importance of maintaining window integrity, stringent codes and regulations have recently been enacted in an attempt to reduce hurricane damage. For example, certain regions of Florida have enacted codes which require windows to pass a flying missile and wind load test before an occupancy certificate will be granted. During the test, windows are impacted by a 9 pound 2 by 4 board travelling at 34 mph. After impact, the windows are subjected to alternating push-pull forces comprising 9,000 inward and outward pressure cycles every 1 to 3 seconds, thereby simulating the alternating forces experienced in a hurricane. The windows must withstand penetration during this test in order to meet the code.
One solution to hurricane-induced window damage is to fit metal storm shutters over the windows. While this approach meets the above-noted code, the shutters must be installed prior to a hurricane. If a building is unattended, or if a storm is not anticipated, the metal shutters may not be installed in time to adequately prevent damage. Furthermore, shuttering of unattended buildings sends a signal to potential burglars and vandals that a building is unoccupied.
Another approach for preventing hurricane damage which meets the above-noted code is the use of window glass laminated with several co-extensive polymeric layers. The polymeric layers include a polyvinyl butyral (PVB) layer attached to the window glass, a polyester middle layer, and an abrasion resistant coating. The composite layers are sold by Dupont under the designation SentryGlas. While window glass laminated with such composite layers meets the above-noted code, the exposed inner surface of the window is relatively susceptible to cuts, abrasions and scratches. Attempts have been made to replace the coextensive abrasion resistant coating with an inner layer of glass in order to improve abrasion resistance. However, windows incorporating such glass inner layers have not adequately prevented penetration, and have not been able to meet the above-noted code.
The present invention has been developed in view of the foregoing, and to overcome other deficiencies of the prior art.